# Functions, operator => eigenfunction, eigenvalue

by sundriedtomato
Tags: eigenfunction, eigenvalue, functions, operator
 P: 12 1. The problem statement, all variables and given/known data Show, that functions f1 = A*sin($$\theta$$)exp[i$$\phi$$] and f2 = B(3cos$$^{2}$$($$\theta$$) - 1) A,B - constants are eigenfunctions of an operator and find eigenvalues 3. The attempt at a solution This is what i got for the first function: The next step is to solve left part of the equation, and than compare it to the right part. The question arises, how to solve that equation? I tried simplifying left part of an equation in mathcad, and I got Next question from that part, is if I am doing it right, how to compare those parts, and answer a question - weather this function is an eigenfunction of an operator? Thank You in advance, and I am constantly near computer and waiting for suggestions.
 P: 777 Your eigen operator has partial derivatives wrt to $\theta$ and $\phi$. When you operate it on your given eigen function, you should get back your original function multiplied by a scaling factor which is your eigenvalue.
 P: 12 Yes, Thank You, but how do I calculate that? May I ask for instructions on how to calculate that left part of an equation? Is the result I got is correct?
HW Helper
P: 2,886

## Functions, operator => eigenfunction, eigenvalue

 Quote by sundriedtomato Yes, Thank You, but how do I calculate that? May I ask for instructions on how to calculate that left part of an equation? Is the result I got is correct?
Just go ahead and apply the derivatives!! It's that simple. (btw, I don't know what you entered in mathcad but what it gave you is wrong).

all you have to do is to apply the derivatives
HW Helper
P: 2,886
 Quote by sundriedtomato Yes, Thank You, but how do I calculate that? May I ask for instructions on how to calculate that left part of an equation? Is the result I got is correct?
For the first term, what you have to calculate is

$$\frac{1}{sin \theta} \frac{\partial}{\partial \theta} ( sin \theta ~\frac{\partial}{ \partial \theta} (A sin \theta} e^{i \phi}}) )$$
 P: 12 I will give it a try right know. Thank You.
 P: 12 So, after proper calculations, the result is Is this one correct? I posted an image of what I am given, and as far as I know, differentiation sign usually is placed before the function? I just don't get it - to what parts of an equation do underlined derivatives belong t? Thank You.
 P: 69 The part in brackets is an "operator"... every incomplete differentiation sign (ie, without anything to differentiate) operates on whatever is "multiplied" to it. For example, the d/d(theta) is your image also operates on A*sin(theta)*exp(i*phi), because when you open the bracket, it gets to differentiate that term. Eg. (the d's are partial) [d/dx + d/dy]*x*y^2 = y^2 + 2*y*x
 P: 12 ....
P: 777
 Quote by sundriedtomato Yes, Thank You, but how do I calculate that? May I ask for instructions on how to calculate that left part of an equation? Is the result I got is correct?
Just operate it on the function. They are simple partial derivatives, I won't take much time to solve. Just a little patience for the initial steps. I tried your problem and many terms get canceled out and you get the solution correctly. You don't need mathcad to do it.
 P: 12 Thank You Reshma! I already managed to solve it correctly, and find eigenvalues as well. For the case with the first function : a = 2h^2, and for the case with second function b = 6h^2. The problem was initially in understanding how to apply operator properly. Once example have been given, and operator properties reanalyzed - problem got solved in like 10 minutes (with putting it all on a paper as well). Thank You everybody who took part in this one!

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